CALCULATION OF THE INTERRUPTION CAPABILITY OF SF6-CF4 AND SF6-C2F6 MIXTURES .1. PLASMA PROPERTIES

For a gas used in circuit breakers, the extinction capability correspo nds roughly to the rate of evolution of the electrical resistance duri ng the are decay. This property is very prominent for SF6 which explai ns its wide use in high-voltage circuit breakers, But in severe winter conditions, this gas may partially liquefy, and some mixtures of SF6 with other gases are considered, The present work deals with a calcula tion of the extinction capability of SF6-CF4 and SF6-C2F6 mixtures, Th is first paper consists of the study of the material functions of the plasma assumed to be in local thermal equilibrium (LTE). The equilibri um composition and the thermodynamic properties have been calculated f rom the partition functions, The transport coefficients have been comp uted by the method of Chapman-Enskog and the net emission coefficient obtained assuming isothermal and homogeneous plasma, CF4 and C2F6 pres ent dissociation phenomena analogous to those of SF6 which leads to si milar variations of mass density, specific heat, and thermal conductiv ity, The electrical conductivities are practically identical for all t he mixtures, The net emission coefficient is enhanced by the presence of carbon in spite of a strong absorption of the resonance lines.